Biodegradable aliphatic-aromatic copolyester for use in nonwoven webs

ABSTRACT

A method for forming a biodegradable aliphatic-aromatic copolyester suitable for use in fibers is provided. In one embodiment, for example, an aliphatic-aromatic copolyester is melt blended with an alcohol to initiate an alcoholysis reaction that results in a copolyester having one or more hydroxyalkyl or alkyl terminal groups. By selectively controlling the alcoholysis conditions (e.g., alcohol and copolymer concentrations, catalysts, temperature, etc.), a modified aliphatic-aromatic copolyester may be achieved that has a molecular weight lower than the starting aliphatic-aromatic polymer. Such lower molecular weight polymers also have the combination of a higher melt flow index and lower apparent viscosity, which is useful in a wide variety of fiber forming applications, such as in the meltblowing of nonwoven webs.

BACKGROUND OF THE INVENTION

Biodegradable nonwoven webs are useful in a wide range of applications,such as in the formation of disposable absorbent products (e.g.,diapers, training pants, sanitary wipes, feminine pads and liners, adultincontinence pads, guards, garments, etc.). To facilitate formation ofthe nonwoven web, a biodegradable polymer should be selected that ismelt processable, yet also has good mechanical and physical properties.Biodegradable aliphatic-aromatic copolyesters have been developed thatpossess good mechanical and physical properties. Although variousattempts have been made to use aliphatic-aromatic copolyesters in theformation of nonwoven webs, their relatively high molecular weight andviscosity have generally restricted their use to only certain types offilm forming processes, but not fiber forming processes. For example,conventional aliphatic-aromatic copolyesters are not typically suitablefor meltblowing processes, which require a low polymer viscosity forsuccessful microfiber formation. As such, a need currently exists for abiodegradable aliphatic-aromatic copolyester that exhibits goodmechanical and physical properties, but which may be readily formed intoa nonwoven web using a variety of techniques (e.g., meltblowing).

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a method forforming a biodegradable polymer for use in fiber formation is disclosed.The method comprises melt blending a first aliphatic-aromaticcopolyester with at least one alcohol so that the copolyester undergoesan alcoholysis reaction. The alcoholysis reaction results in a second,modified copolyester having a melt flow index that is greater than themelt flow index of the first copolyester, determined at a load of 2160grams and temperature of 190° C. in accordance with ASTM Test MethodD1238-E.

In accordance with another embodiment of the present invention, a fiberis disclosed that comprises a biodegradable aliphatic-aromaticcopolyester terminated with an alkyl group, hydroxyalkyl group, or acombination thereof. The copolyester has a melt flow index of from about5 to about 500 grams per 10 minutes, determined at a load of 2160 gramsand temperature of 190° C. in accordance with ASTM Test Method D1238-E.

Other features and aspects of the present invention are discussed ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth more particularly in the remainder of the specification, whichmakes reference to the appended figures in which:

FIG. 1 is a schematic illustration of a process that may be used in oneembodiment of the present invention to form a nonwoven web;

FIG. 2 is a graph depicting apparent viscosity versus various shearrates for the extruded resins of Example 1;

FIG. 3 is a graph depicting apparent viscosity versus various shearrates for the extruded resins of Example 3;

FIG. 4 is a graph depicting apparent viscosity versus various shearrates for the extruded resins of Example 4;

FIG. 5 shows an SEM microphotograph (100×) of a meltblown web formed inExample 5 (32 gsm sample in Table 11); and

FIG. 6 shows an SEM microphotograph (500×) of a meltblown web formed inExample 5 (32 gsm sample in Table 11).

Repeat use of references characters in the present specification anddrawings is intended to represent same or analogous features or elementsof the invention.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

Reference now will be made in detail to various embodiments of theinvention, one or more examples of which are set forth below. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations may be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment, may be used on another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations as come within the scope of theappended claims and their equivalents.

DEFINITIONS

As used herein, the term “biodegradable” or “biodegradable polymer”generally refers to a material that degrades from the action ofnaturally occurring microorganisms, such as bacteria, fungi, and algae;environmental heat; moisture; or other environmental factors. Thebiodegradability of a material may be determined using ASTM Test Method5338.92.

As used herein, the term “fibers” refer to elongated extrudates formedby passing a polymer through a forming orifice such as a die. Unlessnoted otherwise, the term “fibers” includes discontinuous fibers havinga definite length and substantially continuous filaments. Substantiallyfilaments may, for instance, have a length much greater than theirdiameter, such as a length to diameter ratio (“aspect ratio”) greaterthan about 15,000 to 1, and in some cases, greater than about 50,000 to1.

As used herein, the term “monocomponent” refers to fibers formed onepolymer. Of course, this does not exclude fibers to which additives havebeen added for color, anti-static properties, lubrication,hydrophilicity, liquid repellency, etc.

As used herein, the term “multicomponent” refers to fibers formed fromat least two polymers (e.g., bicomponent fibers) that are extruded fromseparate extruders. The polymers are arranged in substantiallyconstantly positioned distinct zones across the cross-section of thefibers. The components may be arranged in any desired configuration,such as sheath-core, side-by-side, pie, island-in-the-sea, and so forth.Various methods for forming multicomponent fibers are described in U.S.Pat. No. 4,789,592 to Taniguchi et al. and U.S. Pat. No. 5,336,552 toStrack et al., U.S. Pat. No. 5,108,820 to Kaneko, et al., U.S. Pat. No.4,795,668 to Kruege, et al., U.S. Pat. No. 5,382,400 to Pike, et al.,U.S. Pat. No. 5,336,552 to Strack, et al., and U.S. Pat. No. 6,200,669to Marmon, et al., which are incorporated herein in their entirety byreference thereto for all purposes. Multicomponent fibers having variousirregular shapes may also be formed, such as described in U.S. Pat. Nos.5,277,976 to Hogle, et al., 5,162,074 to Hills, 5,466,410 to Hills,5,069,970 to Largman, et al., and 5,057,368 to Largman, et al., whichare incorporated herein in their entirety by reference thereto for allpurposes.

As used herein, the term “multiconstituent” refers to fibers formed fromat least two polymers (e.g., biconstituent fibers) that are extrudedfrom the same extruder. The polymers are not arranged in substantiallyconstantly positioned distinct zones across the cross-section of thefibers. Various multiconstituent fibers are described in U.S. Pat. No.5,108,827 to Gessner, which is incorporated herein in its entirety byreference thereto for all purposes.

As used herein, the term “nonwoven web” refers to a web having astructure of individual fibers that are randomly interlaid, not in anidentifiable manner as in a knitted fabric. Nonwoven webs include, forexample, meltblown webs, spunbond webs, carded webs, wet-laid webs,airlaid webs, coform webs, hydraulically entangled webs, etc. The basisweight of the nonwoven web may generally vary, but is typically fromabout 5 grams per square meter (“gsm”) to 200 gsm, in some embodimentsfrom about 10 gsm to about 150 gsm, and in some embodiments, from about15 gsm to about 100 gsm.

As used herein, the term “meltblown” web or layer generally refers to anonwoven web that is formed by a process in which a molten thermoplasticmaterial is extruded through a plurality of fine, usually circular, diecapillaries as molten fibers into converging high velocity gas (e.g.air) streams that attenuate the fibers of molten thermoplastic materialto reduce their diameter, which may be to microfiber diameter.Thereafter, the meltblown fibers are carried by the high velocity gasstream and are deposited on a collecting surface to form a web ofrandomly dispersed meltblown fibers. Such a process is disclosed, forexample, in U.S. Pat. Nos. 3,849,241 to Butin, et al.; 4,307,143 toMeitner, et al.; and 4,707,398 to Wisneski, et al., which areincorporated herein in their entirety by reference thereto for allpurposes. Meltblown fibers may be substantially continuous ordiscontinuous, and are generally tacky when deposited onto a collectingsurface.

As used herein, the term “spunbond” web or layer generally refers to anonwoven web containing small diameter substantially continuousfilaments. The filaments are formed by extruding a molten thermoplasticmaterial from a plurality of fine, usually circular, capillaries of aspinnerette with the diameter of the extruded filaments then beingrapidly reduced as by, for example, eductive drawing and/or otherwell-known spunbonding mechanisms. The production of spunbond webs isdescribed and illustrated, for example, in U.S. Pat. Nos. 4,340,563 toAppel, et al., 3,692,618 to Dorschner, et al., 3,802,817 to Matsuki, etal., 3,338,992 to Kinney, 3,341,394 to Kinney, 3,502,763 to Hartman,3,502,538 to Levv, 3,542,615 to Dobo, et al., and 5,382,400 to Pike, etal., which are incorporated herein in their entirety by referencethereto for all purposes. Spunbond filaments are generally not tackywhen they are deposited onto a collecting surface. Spunbond filamentsmay sometimes have diameters less than about 40 micrometers, and areoften between about 5 to about 20 micrometers.

As used herein, the term “carded web” refers to a web made from staplefibers that are sent through a combing or carding unit, which separatesor breaks apart and aligns the staple fibers in the machine direction toform a generally machine direction-oriented fibrous nonwoven web. Suchfibers are usually obtained in bales and placed in an opener/blender orpicker, which separates the fibers prior to the carding unit. Onceformed, the web may then be bonded by one or more known methods.

As used herein, the term “airlaid web” refers to a web made from bundlesof fibers having typical lengths ranging from about 3 to about 19millimeters (mm). The fibers are separated, entrained in an air supply,and then deposited onto a forming surface, usually with the assistanceof a vacuum supply. Once formed, the web is then bonded by one or moreknown methods.

As used herein, the term “coform web” generally refers to a compositematerial containing a mixture or stabilized matrix of thermoplasticfibers and a second non-thermoplastic material. As an example, coformmaterials may be made by a process in which at least one meltblown diehead is arranged near a chute through which other materials are added tothe web while it is forming. Such other materials may include, but arenot limited to, fibrous organic materials such as woody or non-woodypulp such as cotton, rayon, recycled paper, pulp fluff and alsosuperabsorbent particles, inorganic and/or organic absorbent materials,treated polymeric staple fibers and so forth. Some examples of suchcoform materials are disclosed in U.S. Pat. Nos. 4,100,324 to Anderson,et al.; 5,284,703 to Everhart, et al.; and 5,350,624 to Georger, et al.;which are incorporated herein in their entirety by reference thereto forall purposes.

DETAILED DESCRIPTION

The present invention is directed to a method for forming abiodegradable aliphatic-aromatic copolyester suitable for use in fibers.In one embodiment, for example, an aliphatic-aromatic polymer is meltblended with an alcohol to initiate an alcoholysis reaction that resultsin a copolyester having one or more hydroxyalkyl or alkyl terminalgroups. By selectively controlling the alcoholysis conditions (e.g.,alcohol and copolymer concentrations, catalysts, temperature, etc.), amodified aliphatic-aromatic copolyester may be achieved that has amolecular weight lower than the starting aliphatic-aromatic polymer.Such lower molecular weight polymers also have the combination of ahigher melt flow index and lower apparent viscosity, which is useful ina wide variety of fiber forming applications, such as in the meltblowingof nonwoven webs.

1. Reaction Components

A. Aliphatic-Aromatic Copolyester

The aliphatic-aromatic copolyester may be synthesized using any knowntechnique, such as through the condensation polymerization of a polyolin conjunction with aliphatic and aromatic dicarboxylic acids oranhydrides thereof. The polyols may be substituted or unsubstituted,linear or branched, polyols selected from polyols containing 2 to about12 carbon atoms and polyalkylene ether glycols containing 2 to 8 carbonatoms. Examples of polyols that may be used include, but are not limitedto, ethylene glycol, diethylene glycol, propylene glycol,1,2-propanediol, 1,3-propanediol, 2,2-dimethyl-1,3-propanediol,1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol,1,5-pentanediol, 1,6-hexanediol, polyethylene glycol, diethylene glycol,2,2,4-trimethyl-1,6-hexanediol, thiodiethanol,1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol,2,2,4,4-tetramethyl-1,3-cyclobutanediol, cyclopentanediol, triethyleneglycol, and tetraethylene glycol. Preferred polyols include1,4-butanediol; 1,3-propanediol; ethylene glycol; 1,6-hexanediol;diethylene glycol; and 1,4-cyclohexanedimethanol.

Representative aliphatic dicarboxylic acids that may be used includesubstituted or unsubstituted, linear or branched, non-aromaticdicarboxylic acids selected from aliphatic dicarboxylic acids containing2 to about 12 carbon atoms, and derivatives thereof. Non-limitingexamples of aliphatic dicarboxylic acids include malonic, succinic,oxalic, glutaric, adipic, pimelic, azelaic, sebacic, fumaric,2,2-dimethyl glutaric, suberic, 1,3-cyclopentanedicarboxylic,1,4-cyclohexanedicarboxylic, 1,3-cyclohexanedicarboxylic, diglycolic,itaconic, maleic, and 2,5-norbornanedicarboxylic. Representativearomatic dicarboxylic acids that may be used include substituted andunsubstituted, linear or branched, aromatic dicarboxylic acids selectedfrom aromatic dicarboxylic acids containing 1 to about 6 carbon atoms,and derivatives thereof. Non-limiting examples of aromatic dicarboxylicacids include terephthalic acid, dimethyl terephthalate, isophthalicacid, dimethyl isophthalate, 2,6-napthalene dicarboxylic acid,dimethyl-2,6-naphthalate, 2,7-naphthalenedicarboxylic acid,dimethyl-2,7-naphthalate, 3,4′-diphenyl ether dicarboxylic acid,dimethyl-3,4′-diphenyl ether dicarboxylate, 4,4′-diphenyl etherdicarboxylic acid, dimethyl-4,4′-diphenyl ether dicarboxylate,3,4′-diphenyl sulfide dicarboxylic acid, dimethyl-3,4′-diphenyl sulfidedicarboxylate, 4,4′-diphenyl sulfide dicarboxylic acid,dimethyl-4,4′-diphenyl sulfide dicarboxylate, 3,4′-diphenyl sulfonedicarboxylic acid, dimethyl-3,4′-diphenyl sulfone dicarboxylate,4,4′-diphenyl sulfone dicarboxylic acid, dimethyl-4,4′-diphenyl sulfonedicarboxylate, 3,4′-benzophenonedicarboxylic acid,dimethyl-3,4′-benzophenonedicarboxylate, 4,4′-benzophenonedicarboxylicacid, dimethyl-4,4′-benzophenonedicarboxylate, 1,4-naphthalenedicarboxylic acid, dimethyl-1,4-naphthalate, 4,4′-methylene bis(benzoicacid), dimethyl-4,4′-methylenebis(benzoate), etc., and mixtures thereof.

The polymerization may be catalyzed by a catalyst, such as atitanium-based catalyst (e.g., tetraisopropyltitanate, tetraisopropoxytitanium, dibutoxydiacetoacetoxy titanium, or tetrabutyltitanate). Ifdesired, a diisocyanate chain extender may be reacted with thecopolyester to increase its molecular weight. Representativediisocyanates may include toluene 2,4-diisocyanate, toluene2,6-diisocyanate, 2,4′-diphenylmethane diisocyanate,naphthylene-1,5-diisocyanate, xylylene diisocyanate, hexamethylenediisocyanate (“HMDI”), isophorone diisocyanate andmethylenebis(2-isocyanatocyclohexane). Trifunctional isocyanatecompounds may also be employed that contain isocyanurate and/or biureagroups with a functionality of not less than three, or to replace thediisocyanate compounds partially by tri- or polyisocyanates. Thepreferred diisocyanate is hexamethylene diisocyanate. The amount of thechain extender employed is typically from about 0.3 to about 3.5 wt. %,in some embodiments, from about 0.5 to about 2.5 wt. % based on thetotal weight percent of the polymer.

The copolyesters may either be a linear polymer or a long-chain branchedpolymer. Long-chain branched polymers are generally prepared by using alow molecular weight branching agent, such as a polyol, polycarboxylicacid, hydroxy acid, and so forth. Representative low molecular weightpolyols that may be employed as branching agents include glycerol,trimethylolpropane, trimethylolethane, polyethertriols, glycerol,1,2,4-butanetriol, pentaerythritol, 1,2,6-hexanetriol, sorbitol,1,1,4,4,-tetrakis (hydroxymethyl)cyclohexane, tris(2-hydroxyethyl)isocyanurate, and dipentaerythritol. Representative higher molecularweight polyols (molecular weight of 400 to 3000) that may be used asbranching agents include triols derived by condensing alkylene oxideshaving 2 to 3 carbons, such as ethylene oxide and propylene oxide withpolyol initiators. Representative polycarboxylic acids that may be usedas branching agents include hemimellitic acid, trimellitic(1,2,4-benzenetricarboxylic) acid and anhydride, trimesic(1,3,5-benzenetricarboxylic) acid, pyromellitic acid and anhydride,benzenetetracarboxylic acid, benzophenone tetracarboxylic acid,1,1,2,2-ethane-tetracarboxylic acid, 1,1,2-ethanetricarboxylic acid,1,3,5-pentanetricarboxylic acid, and 1,2,3,4-cyclopentanetetracarboxylicacid. Representative hydroxy acids that may be used as branching agentsinclude malic acid, citric acid, tartaric acid, 3-hydroxyglutaric acid,mucic acid, trihydroxyglutaric acid, 4-carboxyphthalic anhydride,hydroxyisophthalic acid, and 4-(beta-hydroxyethyl)phthalic acid. Suchhydroxy acids contain a combination of 3 or more hydroxyl and carboxylgroups. Especially preferred branching agents include trimellitic acid,trimesic acid, pentaerythritol, trimethylol propane and1,2,4-butanetriol.

The aromatic dicarboxylic acid monomer constituent may be present in thecopolyester in an amount of from about 10 mole % to about 40 mole %, insome embodiments from about 15 mole % to about 35 mole %, and in someembodiments, from about 15 mole % to about 30 mole %. The aliphaticdicarboxylic acid monomer constituent may likewise be present in thecopolyester in an amount of from about 15 mole % to about 45 mole %, insome embodiments from about 20 mole % to about 40 mole %, and in someembodiments, from about 25 mole % to about 35 mole %. The polyol monomerconstituent may also be present in the aliphatic-aromatic copolyester inan amount of from about 30 mole % to about 65 mole %, in someembodiments from about 40 mole % to about 50 mole %, and in someembodiments, from about 45 mole % to about 55 mole %.

In one particular embodiment, for example, the aliphatic-aromaticcopolyester may comprise the following structure:

wherein,

m is an integer from 2 to 10, in some embodiments from 2 to 4, and inone embodiment, 4;

n is an integer from 0 to 18, in some embodiments from 2 to 4, and inone embodiment, 4;

p is an integer from 2 to 10, in some embodiments from 2 to 4, and inone embodiment, 4;

x is an integer greater than 1; and

y is an integer greater than 1. One example of such a copolyester ispolybutylene adipate terephthalate, which is commercially availableunder the designation ECOFLEX® F BX 7011 from BASF Corp. Another exampleof a suitable copolyester containing an aromatic terephtalic acidmonomer constituent is available under the designation ENPOL™ 8060M fromIRE Chemicals (South Korea). Other suitable aliphatic-aromaticcopolyesters may be described in U.S. Pat. Nos. 5,292,783; 5,446,079;5,559,171; 5,580,911; 5,599,858; 5,817,721; 5,900,322; and 6,258,924,which are incorporated herein in their entirety by reference thereto forall purposes.

The aliphatic-aromatic polyester typically has a number averagemolecular weight (“M_(n)”) ranging from about 40,000 to about 120,000grams per mole, in some embodiments from about 50,000 to about 100,000grams per mole, and in some embodiments, from about 60,000 to about85,000 grams per mole. Likewise, the polymer also typically has a weightaverage molecular weight (“M_(w)”) ranging from about 70,000 to about240,000 grams per mole, in some embodiments from about 80,000 to about190,000 grams per mole, and in some embodiments, from about 100,000 toabout 150,000 grams per mole. The ratio of the weight average molecularweight to the number average molecular weight (“M_(w)/M_(n)”), i.e., the“polydispersity index”, is also relatively low. For example, thepolydispersity index typically ranges from about 1.0 to about 3.0, insome embodiments from about 1.2 to about 2.0, and in some embodiments,from about 1.4 to about 1.8. The weight and number average molecularweights may be determined by methods known to those skilled in the art.

The aromatic-aliphatic polyester may also have an apparent viscosity offrom about 100 to about 1000 Pascal seconds (Pass), in some embodimentsfrom about 200 to about 800 Pa·s, and in some embodiments, from about300 to about 600 Pa·s, as determined at a temperature of 170° C. and ashear rate of 1000 sec⁻¹. The melt flow index of the aromatic-aliphaticpolyester may also range from about 0.1 to about 10 grams per 10minutes, in some embodiments from about 0.5 to about 8 grams per 10minutes, and in some embodiments, from about 1 to about 5 grams per 10minutes. The melt flow index is the weight of a polymer (in grams) thatmay be forced through an extrusion rheometer orifice (0.0825-inchdiameter) when subjected to a load of 2160 grams in 10 minutes at acertain temperature (e.g., 190° C.), measured in accordance with ASTMTest Method D1238-E.

The aliphatic-aromatic polymer also typically has a melting point offrom about 50° C. to about 160° C., in some embodiments from about 80°C. to about 160° C., and in some embodiments, from about 10° C. to about140° C. Such low melting point copolyesters are useful in that theybiodegrade at a fast rate and are generally soft. The glass transitiontemperature (“T_(g)”) of the copolyester is also relatively low toimprove flexibility and processability of the polymers. For example, theT_(g) may be about 25° C. or less, in some embodiments about 0° C. orless, and in some embodiments, about −10° C. or less. As discussed inmore detail below, the melting temperature and glass transitiontemperature may be determined using differential scanning calorimetry(“DSC”) in accordance with ASTM D-3417.

B. Alcohol

As indicated above, the aliphatic-aromatic copolyester may be reactedwith an alcohol to form a modified copolyester having a reducedmolecular weight. The concentration of the alcohol reactant mayinfluence the extent to which the molecular weight is altered. Forinstance, higher alcohol concentrations generally result in a moresignificant decrease in molecular weight. Of course, too high of analcohol concentration may also affect the physical characteristics ofthe resulting polymer. Thus, in most embodiments, the alcohol(s) areemployed in an amount of about 0.1 wt. % to about 20 wt. %, in someembodiments from about 0.2 wt. % to about 10 wt. %, and in someembodiments, from about 0.5 wt. % to about 5 wt. %, based on the totalweight of the starting aliphatic-aromatic copolyester.

The alcohol may be monohydric or polyhydric (dihydric, trihydric,tetrahydric, etc.), saturated or unsaturated, and optionally substitutedwith functional groups, such as carboxyl, amine, etc. Examples ofsuitable monohydric alcohols include methanol, ethanol, 1-propanol,2-propanol, 1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 3-pentanol,1-hexanol, 2-hexanol, 3-hexanol, 1-heptanol, 2-heptanol, 3-heptanol,4-heptanol, 1-octanol, 2-octanol, 3-octanol, 4-octanol, 1-nonanol,2-nonanol, 3-nonanol, 4-nonanol, 5-nonanol, 1-decanol, 2-decanol,3-decanol, 4-decanol, 5-decanol, allyl alcohol, 1-butenol, 2-butenol,1-pentenol, 2-pentenol, 1-hexenol, 2-hexenol, 3-hexenol, 1-heptenol,2-heptenol, 3-heptenol, 1-octenol, 2-octenol, 3-octenol, 4-octenol,1-nonenol, 2-nonenol, 3-nonenol, 4-nonenol, 1-decenol, 2-decenol,3-decenol, 4-decenol, 5-decenol, cyclohexanol, cyclopentanol,cycloheptanol, 1-phenylhyl alcohol, 2-phenylhyl alcohol,2-ethoxy-ethanol, methanolamine, ethanolamine, and so forth. Examples ofsuitable dihydric alcohols include 1,3-propanediol, 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol,1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol,1-hydroxymethyl-2-hydroxyethylcyclohexane,1-hydroxy-2-hydroxypropylcyclohexane,1-hydroxy-2-hydroxyethylcyclohexane,1-hydroxymethyl-2-hydroxyethylbenzene,1-hydroxymethyl-2-hydroxypropylbenzene, 1-hydroxy-2-hydroxyethylbenzene,1,2-benzylmethylol, 1,3-benzyldimethylol, and so forth. Suitabletrihydric alcohols may include glycerol, trimethylolpropane, etc., whilesuitable tetrahydric alcohols may include pentaerythritol, erythritol,etc. Preferred alcohols are dihydric alcohols having from 2 to 6 carbonatoms, such as 1,3-propanediol and 1,4-butanediol.

The hydroxy group of the alcohol is generally capable of attacking anester linkage of the aliphatic-aromatic copolyester, thereby leading tochain scission or “depolymerization” of the copolyester molecule intoone or more shorter ester chains. The shorter chains may includealiphatic-aromatic polyesters or oligomers, as well as minor portions ofaliphatic polyesters or oligomers, aromatic polyesters or oligomers, andcombinations of any of the foregoing. Although not necessarily required,the short chain aliphatic-aromatic polyesters formed during alcoholysisare often terminated with an alkyl and/or hydroxyalkyl groups derivedfrom the alcohol. Alkyl group terminations are typically derived frommonohydric alcohols, while hydroxyalkyl group terminations are typicallyderived from polyhydric alcohols. In one particular embodiment, forexample, an aliphatic-aromatic copolyester is formed during thealcoholysis reaction that comprises the following general structure:

wherein,

m is an integer from 2 to 10, in some embodiments from 2 to 4, and inone embodiment, 4;

n is an integer from 0 to 18, in some embodiments from 2 to 4, and inone embodiment, 4;

p is an integer from 2 to 10, in some embodiments from 2 to 4, and inone embodiment, 4;

x is an integer greater than 1;

y is an integer greater than 1; and

R₁ and R₂ are independently selected from hydrogen; hydroxyl groups;straight chain or branched, substituted or unsubstituted C₁-C₁₀ alkylgroups; straight chain or branched, substituted or unsubstituted C₁-C₁₀hydroxalkyl groups. Preferably, at least one of R₁ and R₂, or both, arestraight chain or branched, substituted or unsubstituted, C₁-C₁₀ alkylor C₁-C₁₀ hydroxyalkyl groups, in some embodiments C₁-C₈ alkyl or C₁-C₈hydroxyalkyl groups, and in some embodiments, C₂-C₆ alkyl or C₂-C₆hydroxyalkyl groups. Examples of suitable alkyl and hydroxyalkyl groupsinclude, for instance, methyl, ethyl, iso-propyl, n-propyl, n-butyl,isobutyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl,n-decyl, 1 hydroxyethyl, 2-hydroxyethyl, 3-hydroxypropyl,4-hydroxybutyl, and 5-hydroxypentyl groups. Thus, as indicated, themodified aliphatic-aromatic copolyester has a different chemicalcomposition than an unmodified copolyester in terms of its terminalgroups. The terminal groups may play a substantial role in determiningthe properties of the polymer, such as its reactivity, stability, etc.

Regardless of its particular structure, a new polymer species is formedduring alcoholysis that has a molecular weight lower than that of thestarting polyester. The weight average and/or number average molecularweights may, for instance, each be reduced so that the ratio of thestarting copolyester molecular weight to the new molecular weight is atleast about 1.1, in some embodiments at least about 1.4, and in someembodiments, at least about 1.6. For example, the modifiedaliphatic-aromatic copolyester may have a number average molecularweight (“M_(n)”) ranging from about 10,000 to about 70,000 grams permole, in some embodiments from about 20,000 to about 60,000 grams permole, and in some embodiments, from about 30,000 to about 55,000 gramsper mole. Likewise, the modified copolyester may also have a weightaverage molecular weight (“M_(w)”) of from about 20,000 to about 125,000grams per mole, in some embodiments from about 30,000 to about 110,000grams per mole, and in some embodiments, from about 40,000 to about90,000 grams per mole.

In addition to possessing a lower molecular weight, the modifiedaliphatic-aromatic copolyester may also have a lower apparent viscosityand higher melt flow index than the starting polyester. The apparentviscosity may for instance, be reduced so that the ratio of the startingcopolyester viscosity to the modified copolyester viscosity is at leastabout 1.1, in some embodiments at least about 2, and in someembodiments, from about 10 to about 40. Likewise, the melt flow indexmay be increased so that the ratio of the modified copolyester melt flowindex to the starting copolyester melt flow index is at least about 1.5,in some embodiments at least about 3, in some embodiments at least about50, and in some embodiments, from about 100 to about 1000. In oneparticular embodiment, the modified copolyester may have an apparentviscosity of from about 10 to about 500 Pascal seconds (Pa·s), in someembodiments from about 20 to about 400 Pa·s, and in some embodiments,from about 30 to about 250 Pa·s, as determined at a temperature of 170°C. and a shear rate of 1000 sec⁻¹. The melt flow index (190° C., 2.16kg) of the modified copolyester may range from about 5 to about 500grams per 10 minutes, in some embodiments from about 10 to about 300grams per 10 minutes, and in some embodiments, from about 20 to about250 grams per 10 minutes. Of course, the extent to which the molecularweight, apparent viscosity, and/or melt flow index are altered by thealcoholysis reaction may vary depending on the intended application.

Although differing from the starting polymer in certain properties, themodified copolyester may nevertheless retain other properties of thestarting polymer to enhance the flexibility and processability of thepolymers. For example, the thermal characteristics (e.g., T_(g), T_(m),and latent heat of fusion) typically remain substantially the same asthe starting polymer, such as within the ranges noted above. Further,even though the actual molecular weights may differ, the polydispersityindex of the modified copolyester may remain substantially the same asthe starting polymer, such as within the range of about 1.0 to about3.0, in some embodiments from about 1.1 to about 2.0, and in someembodiments, from about 1.2 to about 1.8.

C. Catalyst

A catalyst may be employed to facilitate the modification of thealcoholysis reaction. The concentration of the catalyst may influencethe extent to which the molecular weight is altered. For instance,higher catalyst concentrations generally result in a more significantdecrease in molecular weight. Of course, too high of a catalystconcentration may also affect the physical characteristics of theresulting polymer. Thus, in most embodiments, the catalyst(s) areemployed in an amount of about 50 to about 2000 parts per million(“ppm”), in some embodiments from about 100 to about 1000 ppm, and insome embodiments, from about 200 to about 1000 ppm, based on the weightof the starting aliphatic-aromatic copolyester.

Any known catalyst may be used in the present invention to accomplishthe desired reaction. In one embodiment, for example, a transition metalcatalyst may be employed, such as those based on Group IVB metals and/orGroup IVA metals (e.g., alkoxides or salts). Titanium-, zirconium-,and/or tin-based metal catalysts are especially desirable and mayinclude, for instance, titanium butoxide, titanium tetrabutoxide,titanium propoxide, titanium isopropoxide, titanium phenoxide, zirconiumbutoxide, dibutyltin oxide, dibutyltin diacetate, tin phenoxide, tinoctylate, tin stearate, dibutyltin dioctoate, dibutyltin dioleylmaleate,dibutyltin dibutylmaleate, dibutyltin dilaurate,1,1,3,3-tetrabutyl-1,3-dilauryloxycarbonyldistannoxane,dibutyltindiacetate, dibutyltin diacetylacetonate, dibutyltinbis(o-phenylphenoxide), dibutyltin bis(triethoxysilicate), dibutyltindistearate, dibutyltin bis(isononyl-3-mercaptopropionate), dibutyltinbis(isooctyl thioglycolate), dioctyltin oxide, dioctyltin dilaurate,dioctyltin diacetate, and dioctyltin diversatate.

D. Co-Solvent

The alcoholysis reaction is typically carried out in the absence of asolvent other than the alcohol reactant. Nevertheless, a co-solvent maybe employed in some embodiments of the present invention. In oneembodiment, for instance, the co-solvent may facilitate the dispersionof the catalyst in the reactant alcohol. Examples of suitableco-solvents may include ethers, such as diethyl ether, anisole,tetrahydrofuran, ethylene glycol dimethyl ether, triethylene glycoldimethyl ether, tetraethylene glycol dimethyl ether, dioxane, etc.;alcohols, such as methanol, ethanol, n-butanol, benzyl alcohol, ethyleneglycol, diethylene glycol, etc.; phenols, such as phenol, etc.;carboxylic acids, such as formic acid, acetic acid, propionic acid,toluic acid, etc.; esters, such as methyl acetate, butyl acetate, benzylbenzoate, etc.; aromatic hydrocarbons, such as benzene, toluene,ethylbenzene, tetralin, etc.; aliphatic hydrocarbons, such as n-hexane,n-octane, cyclohexane, etc.; halogenated hydrocarbons, such asdichloromethane, trichloroethane, chlorobenzene, etc.; nitro compounds,such as nitromethane, nitrobenzene, etc.; carbamides, such asN,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, etc.;ureas, such as N,N-dimethylimidazolidinone, etc.; sulfones, such asdimethyl sulfone, etc.; sulfoxides, such as dimethyl sulfoxide, etc.;lactones, such as butyrolactone, caprolactone, etc.; carbonic acidesters, such as dimethyl carbonate, ethylene carbonate, etc.; and soforth.

When employed, the co-solvent(s) may be employed in an amount from about0.5 wt. % to about 20 wt. %, in some embodiments from about 0.8 wt. % toabout 10 wt. %, and in some embodiments, from about 1 wt. % to about 5wt. %, based on the weight of the reactive composition. It should beunderstood, however, that a co-solvent is not required. In fact, in someembodiments of the present invention, the reactive composition issubstantially free of any co-solvents, e.g., less than about 0.5 wt. %of the reactive composition.

E. Other Ingredients

Other ingredients may of course be utilized for a variety of differentreasons. For instance, a wetting agent may be employed in someembodiments of the present invention to improve hydrophilicity. Wettingagents suitable for use in the present invention are generallycompatible with aliphatic-aromatic copolyesters. Examples of suitablewetting agents may include surfactants, such as UNITHOX® 480 andUNITHOX® 750 ethoxylated alcohols, or UNICID™ acid amide ethoxylates,all available from Petrolite Corporation of Tulsa, Okla. Other suitablewetting agents are described in U.S. Pat. No. 6,177,193 to Tsai, et al.,which is incorporated herein in its entirety by reference thereto forall relevant purposes. Still other materials that may be used include,without limitation, melt stabilizers, processing stabilizers, heatstabilizers, light stabilizers, antioxidants, pigments, surfactants,waxes, flow promoters, plasticizers, particulates, and other materialsadded to enhance processability. When utilized, such additionalingredients are each typically present in an amount of less than about 5wt. %, in some embodiments less than about 1 wt. %, and in someembodiments, less than about 0.5 wt. %, based on the weight of thealiphatic-aromatic copolyester starting polymer.

II. Reaction Technique

The alcoholysis reaction may be performed using any of a variety ofknown techniques. In one embodiment, for example, the reaction isconducted while the starting polymer is in the melt phase (“meltblending”) to minimize the need for additional solvents and/or solventremoval processes. The raw materials (e.g., biodegradable polymer,alcohol, catalyst, etc.) may be supplied separately or in combination(e.g., in a solution). The raw materials may likewise be supplied eithersimultaneously or in sequence to a melt-blending device thatdispersively blends the materials. Batch and/or continuous melt blendingtechniques may be employed. For example, a mixer/kneader, Banbury mixer,Farrel continuous mixer, single-screw extruder, twin-screw extruder,roll mill, etc., may be utilized to blend the materials. Oneparticularly suitable melt-blending device is a co-rotating, twin-screwextruder (e.g., ZSK-30 twin-screw extruder available from Werner &Pfleiderer Corporation of Ramsey, N.J.). Such extruders may includefeeding and venting ports and provide high intensity distributive anddispersive mixing, which facilitate the alcoholysis reaction. Forexample, the copolyester may be fed to a feeding port of the twin-screwextruder and melted. Thereafter, the alcohol may be injected into thepolymer melt. Alternatively, the alcohol may be separately fed into theextruder at a different point along its length. The catalyst, a mixtureof two or more catalysts, or catalyst solutions may be injectedseparately or in combination with the alcohol or a mixture of two ormore alcohols to the polymer melt.

Regardless of the particular melt blending technique chosen, the rawmaterials are blended under high shear/pressure and heat to ensuresufficient mixing for initiating the alcoholysis reaction. For example,melt blending may occur at a temperature of from about 50° C. to about300° C., in some embodiments, from about 70° C. to about 250° C., and insome embodiments, from about 90° C. to about 180° C. Likewise, theapparent shear rate during melt blending may range from about 100seconds⁻¹ to about 10,000 seconds⁻¹, in some embodiments from about 500seconds⁻¹ to about 5000 seconds⁻¹, and in some embodiments, from about800 seconds⁻¹ to about 1200 seconds⁻¹. The apparent shear rate is equalto 4Q/πR³, where Q is the volumetric flow rate (“m³/s”) of the polymermelt and R is the radius (“m”) of the capillary (e.g., extruder die)through which the melted polymer flows.

III. Fiber Formation

Fibers formed from the modified aliphatic-aromatic copolyester maygenerally have any desired configuration, including monocomponent,multicomponent (e.g., sheath-core configuration, side-by-sideconfiguration, pie configuration, island-in-the-sea configuration, andso forth), and/or multiconstituent. In some embodiments, the fibers maycontain one or more strength-enhancing polymers as a component (e.g.,bicomponent) or constituent (e.g., biconstituent) to further enhancestrength and other mechanical properties. The strength-enhancing polymermay be a thermoplastic polymer that is not generally consideredbiodegradable, such as polyolefins, e.g., polyethylene, polypropylene,polybutylene, and so forth; polytetrafluoroethylene; polyesters, e.g.,polyethylene terephthalate, and so forth; polyvinyl acetate; polyvinylchloride acetate; polyvinyl butyral; acrylic resins, e.g., polyacrylate,polymethylacrylate, polymethylmethacrylate, and so forth; polyamides,e.g., nylon; polyvinyl chloride; polyvinylidene chloride; polystyrene;polyvinyl alcohol; and polyurethanes. More desirably, however, thestrength-enhancing polymer is biodegradable, such as aliphaticpolyesters, such as polyesteramides, modified polyethyleneterephthalate, polylactic acid (PLA) and its copolymers, terpolymersbased on polylactic acid, polyglycolic acid, polyalkylene carbonates(such as polyethylene carbonate), polyhydroxyalkanoates (PHA),polyhydroxybutyrates (PHB), polyhydroxyvalerates (PHV),polyhydroxybutyrate-hydroxyvalerate copolymers (PHBV), andpolycaprolactone, and succinate-based aliphatic polymers (e.g.,polybutylene succinate, polybutylene succinate adipate, and polyethylenesuccinate); aromatic polyesters; or other aliphatic-aromaticcopolyesters.

Any of a variety of processes may be used to form fibers in accordancewith the present invention. Referring to FIG. 1, for example, oneembodiment of a method for forming meltblown fibers is shown. Meltblownfibers form a structure having a small average pore size, which may beused to inhibit the passage of liquids and particles, while allowinggases (e.g., air and water vapor) to pass therethrough. To achieve thedesired pore size, the meltblown fibers are typically “microfibers” inthat they have an average size of 10 micrometers or less, in someembodiments about 7 micrometers or less, and in some embodiments, about5 micrometers or less. The ability to produce such fine fibers may befacilitated in the present invention through the use of a modifiedcopolyester having the desirable combination of low apparent viscosityand high melt flow index.

In FIG. 1, for instance, the raw materials (e.g., polymer, alcohol,catalyst, etc.) are fed into an extruder 12 from a hopper 10. The rawmaterials may be provided to the hopper 10 using any conventionaltechnique and in any state. For example, the alcohol may be supplied asa vapor or liquid. Alternatively, the aliphatic-aromatic copolyester maybe fed to the hopper 10, and the alcohol and optional catalyst (eitherin combination or separately) may be injected into the copolyester meltin the extruder 12 downstream from the hopper 10. The extruder 12 isdriven by a motor 11 and heated to a temperature sufficient to extrudethe polymer and to initiate the alcoholysis reaction. For example, theextruder 12 may employ one or multiple zones operating at a temperatureof from about 50° C. to about 300° C., in some embodiments, from about70° C. to about 250° C., and in some embodiments, from about 90° C. toabout 180° C. Typical shear rates range from about 100 seconds⁻¹ toabout 10,000 seconds-1, in some embodiments from about 500 seconds⁻¹ toabout 5000 seconds⁻¹, and in some embodiments, from about 800 seconds⁻¹to about 1200 seconds⁻¹.

Once formed, the modified aliphatic-aromatic copolyester may besubsequently fed to another extruder in a fiber formation line (e.g.,extruder 12 of a meltblown spinning line). Alternatively, the modifiedaliphatic-aromatic copolymer may be directly formed into a fiber throughsupply to a die 14, which may be heated by a heater 16. It should beunderstood that other meltblown die tips may also be employed. As thepolymer exits the die 14 at an orifice 19, high pressure fluid (e.g.,heated air) supplied by conduits 13 attenuates and spreads the polymerstream into microfibers 18. Although not shown in FIG. 1, the die 14 mayalso be arranged adjacent to or near a chute through which othermaterials (e.g., cellulosic fibers, particles, etc.) traverse tointermix with the extruded polymer and form a “coform” web.

The microfibers 18 are randomly deposited onto a foraminous surface 20(driven by rolls 21 and 23) with the aid of an optional suction box 15to form a meltblown web 22. The distance between the die tip and theforaminous surface 20 is generally small to improve the uniformity ofthe fiber laydown. For example, the distance may be from about 1 toabout 35 centimeters, and in some embodiments, from about 2.5 to about15 centimeters. In FIG. 1, the direction of the arrow 28 shows thedirection in which the web is formed (i.e., “machine direction”) andarrow 30 shows a direction perpendicular to the machine direction (i.e.,“cross-machine direction”). Optionally, the meltblown web 22 may then becompressed by rolls 24 and 26. The desired denier of the fibers may varydepending on the desired application. Typically, the fibers are formedto have a denier per filament of less than about 6, in some embodimentsless than about 3, and in some embodiments, from about 0.5 to about 3.In addition, the fibers generally have an average diameter of from about0.1 to about 20 micrometers, in some embodiments from about 0.5 to about15 micrometers, and in some embodiments, from about 1 to about 10micrometers.

Once formed, the nonwoven web may then be bonded using any conventionaltechnique, such as with an adhesive or autogeneously (e.g., fusionand/or self-adhesion of the fibers without an applied externaladhesive). Autogenous bonding, for instance, may be achieved throughcontact of the fibers while they are semi-molten or tacky, or simply byblending a tackifying resin and/or solvent with the aliphaticpolyester(s) used to form the fibers. Suitable autogenous bondingtechniques may include ultrasonic bonding, thermal bonding, through-airbonding, and so forth.

For instance, the web may be passed through a nip formed between a pairof rolls, one or both of which are heated to melt-fuse the fibers. Oneor both of the rolls may also contain intermittently raised bond pointsto provide an intermittent bonding pattern. The pattern of the raisedpoints is generally selected so that the nonwoven web has a total bondarea of less than about 50% (as determined by conventional opticalmicroscopic methods), and in some embodiments, less than about 30%.Likewise, the bond density is also typically greater than about 100bonds per square inch, and in some embodiments, from about 250 to about500 pin bonds per square inch. Such a combination of total bond area andbond density may be achieved by bonding the web with a pin bond patternhaving more than about 100 pin bonds per square inch that provides atotal bond surface area less than about 30% when fully contacting asmooth anvil roll. In some embodiments, the bond pattern may have a pinbond density from about 250 to about 350 pin bonds per square inch and atotal bond surface area from about 10% to about 25% when contacting asmooth anvil roll. Exemplary bond patterns include, for instance, thosedescribed in U.S. Pat. No. 3,855,046 to Hansen et al., U.S. Pat. No.5,620,779 to Levy et al., U.S. Pat. No. 5,962,112 to Haynes et al., U.S.Pat. No. 6,093,665 to Sayovitz et al., U.S. Design Pat. No. 428,267 toRomano et al. and U.S. Design Pat. No. 390,708 to Brown, which areincorporated herein in their entirety by reference thereto for allpurposes.

Due to the particular rheological and thermal properties of the modifiedaliphatic-aromatic copolyester used to form the fibers, the web bondingconditions (e.g., temperature and nip pressure) may be selected to causethe polymer to melt and flow at relatively low temperatures. Forexample, the bonding temperature (e.g., the temperature of the rollers)may be from about 50° C. to about 160° C., in some embodiments fromabout 80° C. to about 160° C., and in some embodiments, from about 100°C. to about 140° C. Likewise, the nip pressure may range from about 5 toabout 150 pounds per square inch, in some embodiments, from about 10 toabout 100 pounds per square inch, and in some embodiments, from about 30to about 60 pounds per square inch.

In addition to meltblown webs, a variety of other nonwoven webs may alsobe formed from the modified aliphatic-aromatic copolyester in accordancewith the present invention, such as spunbond webs, bonded carded webs,wet-laid webs, airlaid webs, coform webs, hydraulically entangled webs,etc. For example, the polymer may be extruded through a spinnerette,quenched and drawn into substantially continuous filaments, and randomlydeposited onto a forming surface. Alternatively, the polymer may beformed into a carded web by placing bales of fibers formed from theblend into a picker that separates the fibers. Next, the fibers are sentthrough a combing or carding unit that further breaks apart and alignsthe fibers in the machine direction so as to form a machinedirection-oriented fibrous nonwoven web. Once formed, the nonwoven webis typically stabilized by one or more known bonding techniques.

The fibers of the present invention may constitute the entire fibrouscomponent of the nonwoven web or blended with other types of fibers(e.g., staple fibers, filaments, etc). When blended with other types offibers, it is normally desired that the fibers of the present inventionconstitute from about 20 wt % to about 95 wt. %, in some embodimentsfrom about 30 wt. % to about 90 wt. %, and in some embodiments, fromabout 40 wt. % to about 80 wt. % of the total amount of fibers employedin the nonwoven web. For example, additional monocomponent and/ormulticomponent synthetic fibers may be utilized in the nonwoven web.Some suitable polymers that may be used to form the synthetic fibersinclude, but are not limited to: polyolefins, e.g., polyethylene,polypropylene, polybutylene, and so forth; polytetrafluoroethylene;polyesters, e.g., polyethylene terephthalate and so forth; polyvinylacetate; polyvinyl chloride acetate; polyvinyl butyral; acrylic resins,e.g., polyacrylate, polymethylacrylate, polymethylmethacrylate, and soforth; polyamides, e.g., nylon; polyvinyl chloride; polyvinylidenechloride; polystyrene; polyvinyl alcohol; polyurethanes; polylacticacid; etc. If desired, biodegradable polymers, such as poly(glycolicacid) (PGA), poly(lactic acid) (PLA), poly(β-malic acid) (PMLA),poly(ε-caprolactone) (PCL), poly(ρ-dioxanone) (PDS), poly(butylenesuccinate) (PBS), and poly(3-hydroxybutyrate) (PHB), may also beemployed. Some examples of known synthetic fibers include sheath-corebicomponent fibers available from KoSa Inc. of Charlotte, N.C. under thedesignations T-255 and T-256, both of which use a polyolefin sheath, orT-254, which has a low melt co-polyester sheath. Still other knownbicomponent fibers that may be used include those available from theChisso Corporation of Moriyama, Japan or Fibervisions LLC of Wilmington,Del. Synthetic or natural cellulosic polymers may also be used,including but not limited to, cellulosic esters; cellulosic ethers;cellulosic nitrates; cellulosic acetates; cellulosic acetate butyrates;ethyl cellulose; regenerated celluloses, such as viscose, rayon, and soforth.

The fibers of the present invention may also be blended with pulpfibers, such as high-average fiber length pulp, low-average fiber lengthpulp, or mixtures thereof. One example of suitable high-average lengthfluff pulp fibers includes softwood kraft pulp fibers. Softwood kraftpulp fibers are derived from coniferous trees and include pulp fiberssuch as, but not limited to, northern, western, and southern softwoodspecies, including redwood, red cedar, hemlock, Douglas fir, true firs,pine (e.g., southern pines), spruce (e.g., black spruce), combinationsthereof, and so forth. Northern softwood kraft pulp fibers may be usedin the present invention. An example of commercially available southernsoftwood kraft pulp fibers suitable for use in the present inventioninclude those available from Weyerhaeuser Company with offices inFederal Way, Wash. under the trade designation of “NB-416.” Anothersuitable pulp for use in the present invention is a bleached, sulfatewood pulp containing primarily softwood fibers that is available fromBowater Corp. with offices in Greenville, S.C. under the trade nameCoosAbsorb S pulp. Low-average length fibers may also be used in thepresent invention. An example of suitable low-average length pulp fibersis hardwood kraft pulp fibers. Hardwood kraft pulp fibers are derivedfrom deciduous trees and include pulp fibers such as, but not limitedto, eucalyptus, maple, birch, aspen, etc. Eucalyptus kraft pulp fibersmay be particularly desired to increase softness, enhance brightness,increase opacity, and change the pore structure of the sheet to increaseits wicking ability.

Nonwoven laminates may also be formed in which one or more layers areformed from the modified aliphatic-aromatic copolyester of the presentinvention. In one embodiment, for example, the nonwoven laminatecontains a meltblown layer positioned between two spunbond layers toform a spunbond/meltblown/spunbond (“SMS”) laminate. If desired, themeltblown layer may be formed from the modified aliphatic-aromaticcopolyester. The spunbond layer may be formed from the modifiedcopolyester, other biodegradable polymer(s), and/or any other polymer(e.g., polyolefins). Various techniques for forming SMS laminates aredescribed in U.S. Pat. Nos. 4,041,203 to Brock et al.; 5,213,881 toTimmons, et al.; 5,464,688 to Timmons, et al.; 4,374,888 to Bornslaeger;5,169,706 to Collier, et al.; and 4,766,029 to Brock et al., as well asU.S. Patent Application Publication No. 2004/0002273 to Fitting, et al.,all of which are incorporated herein in their entirety by referencethereto for all purposes. Of course, the nonwoven laminate may haveother configuration and possess any desired number of meltblown andspunbond layers, such as spunbond/meltblown/meltblown/spunbond laminates(“SMMS”), spunbond/meltblown laminates (“SM”), etc. Although the basisweight of the nonwoven laminate may be tailored to the desiredapplication, it generally ranges from about 10 to about 300 grams persquare meter (“gsm”), in some embodiments from about 25 to about 200gsm, and in some embodiments, from about 40 to about 150 gsm.

If desired, the nonwoven web or laminate may be applied with varioustreatments to impart desirable characteristics. For example, the web maybe treated with liquid-repellency additives, antistatic agents,surfactants, colorants, antifogging agents, fluorochemical blood oralcohol repellents, lubricants, and/or antimicrobial agents. Inaddition, the web may be subjected to an electret treatment that impartsan electrostatic charge to improve filtration efficiency. The charge mayinclude layers of positive or negative charges trapped at or near thesurface of the polymer, or charge clouds stored in the bulk of thepolymer. The charge may also include polarization charges that arefrozen in alignment of the dipoles of the molecules. Techniques forsubjecting a fabric to an electret treatment are well known by thoseskilled in the art. Examples of such techniques include, but are notlimited to, thermal, liquid-contact, electron beam and corona dischargetechniques. In one particular embodiment, the electret treatment is acorona discharge technique, which involves subjecting the laminate to apair of electrical fields that have opposite polarities. Other methodsfor forming an electret material are described in U.S. Pat. Nos.4,215,682 to Kubik. et al.; 4,375,718 to Wadsworth; 4,592,815 to Nakao;4,874,659 to Ando; 5,401,446 to Tsai, et al.; 5,883,026 to Reader, etal.; 5,908,598 to Rousseau, et al.; 6,365,088 to Knight, et al., whichare incorporated herein in their entirety by reference thereto for allpurposes.

The nonwoven web or laminate may be used in a wide variety ofapplications. For example, the web may be incorporated into a “medicalproduct”, such as gowns, surgical drapes, facemasks, head coverings,surgical caps, shoe coverings, sterilization wraps, warming blankets,heating pads, and so forth. Of course, the nonwoven web may also be usedin various other articles. For example, the nonwoven web may beincorporated into an “absorbent article” that is capable of absorbingwater or other fluids. Examples of some absorbent articles include, butare not limited to, personal care absorbent articles, such as diapers,training pants, absorbent underpants, incontinence articles, femininehygiene products (e.g., sanitary napkins), swim wear, baby wipes, mittwipe, and so forth; medical absorbent articles, such as garments,fenestration materials, underpads, bedpads, bandages, absorbent drapes,and medical wipes; food service wipers; clothing articles; pouches, andso forth. Materials and processes suitable for forming such articles arewell known to those skilled in the art. Absorbent articles, forinstance, typically include a substantially liquid-impermeable layer(e.g., outer cover), a liquid-permeable layer (e.g., bodyside liner,surge layer, etc.), and an absorbent core. In one embodiment, forexample, the nonwoven web of the present invention may be used to forman outer cover of an absorbent article.

The present invention may be better understood with reference to thefollowing examples.

Test Methods

Molecular Weight:

The molecular weight distribution of a polymer was determined by gelpermeation chromatography (“GPC”). The samples were initially preparedby adding 0.5% wt/v solutions of the sample polymers in chloroform to40-milliliter glass vials. For example, 0.05±0.0005 grams of the polymerwas added to 10 milliliters of chloroform. The prepared samples wereplaced on an orbital shaker and agitated overnight. The dissolved samplewas filtered through a 0.45-micrometer PTFE membrane and analyzed usingthe following conditions:

-   Columns: Styragel HR 1, 2, 3, 4, & 5E (5 in series) at 41° C.-   Solvent/Eluent: Chloroform @1.0 milliliter per minute-   HPLC: Waters 600E gradient pump and controller, Waters 717 auto    sampler-   Detector: Waters 2414 Differential Refractometer at sensitivity=30,    at 40° C. and scale factor of 20-   Sample Concentration: 0.5% of polymer “as is”-   Injection Volume: 50 microliters-   Calibration Standards Narrow MW polystyrene, 30-microliter injected    volume.

Number Average Molecular Weight (MW_(n)), Weight Average MolecularWeight (MW_(w)) and first moment of viscosity average molecular weight(MW_(z)) were obtained.

Apparent Viscosity:

The rheological properties of polymer samples were determined using aGötffert Rheograph 2003 capillary rheometer with WinRHEO version 2.31analysis software. The setup included a 2000-bar pressure transducer anda 30/1:0/180 roundhole capillary die. Sample loading was done byalternating between sample addition and packing with a ramrod. A2-minute melt time preceded each test to allow the polymer to completelymelt at the test temperature (usually 160 to 220° C.). The capillaryrheometer determined the apparent viscosity (Pa·s) at various shearrates, such as 100, 200, 500, 1000, 2000, and 4000 s⁻¹. The resultantrheology curve of apparent shear rate versus apparent viscosity gave anindication of how the polymer would run at that temperature in anextrusion process.

Melt Flow Index:

The melt flow index is the weight of a polymer (in grams) forced throughan extrusion rheometer orifice (0.0825-inch diameter) when subjected toa load of 2160 grams in 10 minutes, typically at 190° C. Unlessotherwise indicated, the melt flow index was measured in accordance withASTM Test Method D1238-E.

Thermal Properties:

The melting temperature (“T_(m)”), glass transition temperature(“T_(g)”), and latent heat of fusion (“ΔH_(f)”) were determined bydifferential scanning calorimetry (DSC). The differential scanningcalorimeter was a THERMAL ANALYST 2910 Differential ScanningCalorimeter, which was outfitted with a liquid nitrogen coolingaccessory and with a THERMAL ANALYST 2200 (version 8.10) analysissoftware program, both of which are available from T.A. Instruments Inc.of New Castle, Del. To avoid directly handling the samples, tweezers orother tools were used. The samples were placed into an aluminum pan andweighed to an accuracy of 0.01 milligram on an analytical balance. A lidwas crimped over the material sample onto the pan. Typically, the resinpellets were placed directly in the weighing pan, and the fibers werecut to accommodate placement on the weighing pan and covering by thelid.

The differential scanning calorimeter was calibrated using an indiummetal standard and a baseline correction was performed, as described inthe operating manual for the differential scanning calorimeter. Amaterial sample was placed into the test chamber of the differentialscanning calorimeter for testing, and an empty pan is used as areference. All testing was run with a 55-cubic centimeter per minutenitrogen (industrial grade) purge on the test chamber. For resin pelletsamples, the heating and cooling program was a 2-cycle test that beganwith an equilibration of the chamber to −50° C., followed by a firstheating period at a heating rate of 10° C. per minute to a temperatureof 200° C., followed by equilibration of the sample at 200° C. for 3minutes, followed by a first cooling period at a cooling rate of 20° C.per minute to a temperature of −50° C., followed by equilibration of thesample at −50° C. for 3 minutes, and then a second heating period at aheating rate of 10° C. per minute to a temperature of 200° C. For fibersamples, the heating and cooling program was a 1-cycle test that beganwith an equilibration of the chamber to −50° C., followed by a heatingperiod at a heating rate of 20° C. per minute to a temperature of 200°C., followed by equilibration of the sample at 200° C. for 3 minutes,and then a cooling period at a cooling rate of 10° C. per minute to atemperature of −50° C. All testing was run with a 55-cubic centimeterper minute nitrogen (industrial grade) purge on the test chamber.

The results were then evaluated using the THERMAL ANALYST 2200 analysissoftware program, which identified and quantified the glass transitiontemperature of inflection, the endothermic and exothermic peaks, and theareas under the peaks on the DSC plots. The glass transition temperaturewas identified as the region on the plot-line where a distinct change inslope occurred, and the melting temperature was determined using anautomatic inflection calculation. The areas under the peaks on the DSCplots were determined in terms of joules per gram of sample (J/g). Forexample, the endothermic heat of melting of a resin or fiber sample wasdetermined by integrating the area of the endothermic peak. The areavalues were determined by converting the areas under the DSC plots (e.g.the area of the endotherm) into the units of joules per gram (J/g) usingcomputer software.

Tensile Properties:

The strip tensile strength values were determined in substantialaccordance with ASTM Standard D-5034. Specifically, a nonwoven websample was cut or otherwise provided with size dimensions that measured25 millimeters (width)×127 millimeters (length). Aconstant-rate-of-extension type of tensile tester was employed. Thetensile testing system was a Sintech Tensile Tester, which is availablefrom Sintech Corp. of Cary, N.C. The tensile tester was equipped withTESTWORKS 4.08B software from MTS Corporation to support the testing. Anappropriate load cell was selected so that the tested value fell withinthe range of 10-90% of the full scale load. The sample was held betweengrips having a front and back face measuring 25.4 millimeters×76millimeters. The grip faces were rubberized, and the longer dimension ofthe grip was perpendicular to the direction of pull. The grip pressurewas pneumatically maintained at a pressure of 40 pounds per square inch.The tensile test was run at a 300-millimeter per minute rate with agauge length of 10.16 centimeters and a break sensitivity of 40%.

Five samples were tested by applying the test load along themachine-direction and five samples were tested by applying the test loadalong the cross direction. In addition to tensile strength, the peakload, peak elongation (i.e., % strain at peak load), and the energy topeak were measured. The peak strip tensile loads from each specimentested were arithmetically averaged to determine the MD or CD tensilestrength.

Example 1

An aliphatic-aromatic copolyester resin was initially obtained from BASFunder the designation ECOFLEX® F BX 7011. The copolyester resin wasmodified by melt blending with a reactant solution. For Samples 1 and 4(see Table 1), the reactant solution contained 89 wt. % 1,4-butanedioland 11 wt. % acetone. For Samples 2, 3, 5, and 6 (see Table 1), thereactant solution contained 87 wt. % 1,4-butanediol, 11 wt. % acetone,and 2 wt. % dibutyltin diacetate (the catalyst). The solution was fed byan Eldex pump to a liquid injection port located at barrel #4 of aco-rotating, twin-screw extruder (USALAB Prism H16, diameter: 16 mm, L/Dof 40/1) manufactured by Thermo Electron Corporation. The resin was fedto the twin screw extruder at barrel #1. The screw length was 25 inches.The extruder had one die opening having a diameter of 3 millimeters.Upon formation, the extruded resin was cooled on a fan-cooled conveyorbelt and formed into pellets by a Conair pelletizer. Reactive extrusionparameters were monitored on the USALAB Prism H16 extruder during thereactive extrusion process. The conditions are shown below in Table 1.

TABLE 1 Reactive Extrusion Process Conditions for modifying Ecoflex F BX7011 on a USALAB Prism H16 Screw Resin Reactant Sample Temperature (°C.) Speed Rate (% of No. Zone 1, 2, 3-8, 9, 10 (rpm) (lb/h) resin rate)F BX 90 125 165 125 110 150 2.6 0 7011 1 90 125 165 125 110 150 2.6 4(No catalyst) 2 90 125 165 125 110 150 2.6 4 3 90 125 180 125 110 1502.6 4 4 90 125 190 125 110 150 2.6 4 (No catalyst) 5 90 125 190 125 110150 2.6 4 6 90 125 200 125 110 150 2.6 4

The melt rheology was studied for the unmodified ECOFLEX® F BX 7011 andSamples 1-6 (modified with 1,4 butanediol). The measurement was carriedout on a Göettfert Rheograph 2003 (available from Göettfert of RockHill, S.C.) at 170° C. with a 30/1 (Length/Diameter) mm/mm die. Theapparent melt viscosity was determined at apparent shear rates of 100,200, 500, 1000, 2000 and 5000 s⁻¹. The apparent melt viscosities at thevarious apparent shear rates were plotted and the rheology curves weregenerated as shown in FIG. 2. As illustrated, the apparent viscosity ofthe control sample (unmodified ECOFLEX® resin) was much higher than theapparent viscosities of Samples 1-6. The melt flow indices of thesamples were also determined with a Tinius Olsen Extrusion plastometer(170° C., 2.16 kg). Further, the samples were subjected to molecularweight (MW) analysis by GPC with narrow MW distribution polystyrenes asstandards. The results are set forth below in Table 2.

TABLE 2 Properties of modified Ecoflex F BX 7011 on a USALAB Prism H16Apparent Viscosity Melt (Pa · s at Flow rate apparent) (g/10 min AverageMol. Wt Poly- Sample shear rate of at 170° C. (g/mol) dispersity No.1000/s) and 2.16 kg) Mw Mn (Mw/Mn) F BX 7011 498 1.65 125206 73548 1.7 1365 9.6 114266 67937 1.68 2 51 230 77391 41544 1.86 3 37 377 71072 397671.79 4 241 14 109317 66507 1.64 5 38 475 65899 35529 1.85 6 22 571 5680929316 1.94

As indicated, the melt flow indices of the modified resins (Samples 1-6)were significantly greater than the control sample. In addition, theweight average molecular weight (M_(w)) and number average molecularweight (M_(n)) were decreased in a controlled fashion, which confirmedthat the increase in melt flow index was due to alcoholysis withbutanediol. The resulting modified aliphatic-aromatic copolyesters hadhydroxybutyl terminal groups.

Example 2

The modification of ECOFLEX® F BX 7011 by monohydric alcohols wasdemonstrated with 1-butanol, 2-propanol, and 2-ethoxy-ethanol asexamples of monohydric alcohols. The experimental set-up was the same asdescribed in Example 1. The process conditions are shown in Table 3.Dibutyltin diacetate was the catalyst used. As shown in Table 3, thetorque decreased as monohydric alcohol was fed to the extruder. Thetorque was further decreased as monohydric alcohol and catalyst wereboth fed to the extruder.

TABLE 3 Reactive Extrusion Conditions for modifying Ecoflex F BX 7011 ona USALAB Prism H16 with monohydric alcohols Sample Temperature (° C.)Screw Speed Resin Rate Reactant Catalyst Torque I.D. Zone 1, 2, 3-8, 9,10 (rpm) (lb/h) (% of resin rate) (% of resin rate) (%) F BX 7011 90 125180 125 110 150 2.5 0 0 >100 7 90 125 180 125 110 150 2.5 3.4%,2-Propanol 0 90 8 90 125 180 125 110 150 2.5 3.4%, 2-Propanol 0.1 80 990 125 180 125 110 150 2.5 3.6%, 1-Butanol 0 72 10 90 125 180 125 110150 2.5 3.6%, 1-Butanol 0.1 54 11 90 125 180 125 110 150 2.5   4%,2-Ethoxy-ethanol 0 64 12 90 125 180 125 110 150 2.5   4%,2-Ethoxy-ethanol 0.1 58

The apparent viscosity and molecular weight were determined for eachsample as described in Example 1. The results are shown below in Table4.

TABLE 4 Properties of modified Ecoflex F BX 7011 with monohydricalcohols on a USALAB Prism H16 Apparent Viscosity Average Mol. Poly-Sample (Pa · s at apparent Wt (g/mol) dispersity I.D. shear rate of 10001/s) Mw Mn (Mw/Mn) F BX 7011 376 128100 77200 1.66 7 364 120800 718001.68 8 273 115000 69400 1.66 9 292 115900 70800 1.64 10 126 89800 510001.76 11 324 116800 71000 1.64 12 215 104100 60500 1.72

As indicated, Samples 7-12 had lower apparent viscosities and molecularweights over the entire range of shear rates than the control sample.The resulting modified copolyesters had alkyl terminal groups that arecompositionally different than the unmodified copolyester.

Example 3

Modification of ECOFLEX® F BX 7011 with 1,4-butanediol was performed asdescribed in Example 1 using titanium propoxide (“Ti-P”), titaniumbutoxide (“Ti-B”) and titanium isopropoxide (“Ti-IsoP”) catalysts.During the reactive extrusion process, the torques of the extruder weremoderately decreased with the addition of only 1,4-butanediol, andfurther decreased with the addition of the titanium catalysts. Theprocess conditions are shown in Table 5. The resulting modifiedcopolyesters have hydroxybutyl terminal groups.

TABLE 5 Reactive Extrusion Process Conditions for modifying Ecoflex F BX7011 on a USALAB Prism H16 with 1,4-butanediol and titanium catalystsSample Temperature (° C.) Screw Speed Resin Rate 1,4-butanediol CatalystTorque I.D. Zone 1, 2, 3-8, 9, 10 (rpm) (lb/h) (% of resin rate) (ppm ofresin rate) (%) F BX 7011 95 145 180 130 100 150 3 0  0 >100 13 95 145180 130 100 150 3 2  0 85 14 95 145 180 130 100 150 3 3.5  0 75 15 95145 180 130 100 150 3 2 400, Ti-P 69 16 95 145 180 130 100 150 3 3.5700, Ti-P 48 17 95 145 180 130 100 150 3 2 400, Ti-B 76 18 95 145 180130 100 150 3 3.5 700, Ti-B 55 19 95 145 180 130 100 150 3 2 400,Ti-IsoP 79 20 95 145 180 130 100 150 3 3.5 700, Ti-IsoP 64

The apparent viscosity and molecular weight were determined for eachsample as described in Example 1. The results are shown in FIG. 3 andTable 6.

TABLE 6 Properties of modified Ecoflex F BX 7011 with monohydricalcohols on a USALAB Prism H16 Apparent Viscosity Average Mol. Poly-Sample (Pa · s at apparent Wt (g/mol) dispersity I.D. shear rate of 10001/s) Mw Mn (Mw/Mn) F BX 7011 376 128100 77200 1.66 13 297 112800 710001.7 14 219 102000 60100 1.83 15 198 97050 57050 1.74 16 60 69100 376001.67 17 218 103700 61800 1.6 18 95 89900 51600 1.7 19 243 110200 641001.68 20 87 100300 59900 1.72

As shown in FIG. 3, the viscosity of Sample 16 (titanium propoxidecatalyst) was significant lower than Sample 14 (no catalyst) over theentire range of shear rates. In addition, the molecular weights ofSamples 13-20 were less than the control sample.

Example 4

An aliphatic-aromatic copolyester resin was obtained from BASF under thedesignation ECOFLEX® F BX 7011. A reactant solution contained 87.5 wt. %1,4-butanediol, 7.5 wt. % ethanol, and 5 wt. % titanium propoxide wasmade. A co-rotating, twin-screw extruder was employed (ZSK-30, diameterof 30 millimeters) that was manufactured by Werner and PfleidererCorporation of Ramsey, N.J. The screw length was 1328 millimeters. Theextruder had 14 barrels, numbered consecutively 1-14 from the feedhopper to the die. The first barrel (#1) received the ECOFLEX® BFX 7011resin via a volumetric feeder at a throughput of 30 pounds per hour. Thefifth barrel (#5) received the reactant solution via a pressurizedinjector connected with an Eldex pump at a final rate of 0 to 1 wt. %1,4-butanediol and 0 to 700 parts per million (“ppm”) titaniumpropoxide, respectively. The screw speed was 150 revolutions per minute(“rpm”). The die used to extrude the resin had 4 die openings (6millimeters in diameter) that were separated by 3 millimeters. Uponformation, the extruded resin was cooled on a fan-cooled conveyor beltand formed into pellets by a Conair pelletizer. Reactive extrusionparameters were monitored during the reactive extrusion process. Theconditions are shown below in Table 7.

TABLE 7 Process Conditions for Reactive Extrusion of Ecoflex F BX 7011with 1,4-Butanediol on a ZSK-30 Extruder Reactants Resin TitaniumExtruder Extruder temperature profile Samples feeding rate ButanediolPropoxide speed (° C.) Torque No. (lb/h) (%) (ppm) (rpm) T₁ T₂ T₃ T₄ T₅T₆ T₇ T_(melt) P_(melt) (%) F BX 7011 30 0 0 150 160 170 185 185 185 185100 116 400 >100 21 30 1 0 150 160 171 184 185 185 185 100 108 300 >10022 30 0.75 375 150 160 170 185 185 185 185 100 110 70 85-90 23 30 1 700150 160 170 185 185 185 185 100 110 30 66-72

As indicated, the addition of 1 wt. % butanediol alone (Sample 21) didnot significantly decrease the torque of the control sample, althoughthe die pressure did drop from 300 to 130 pounds per square inch(“psi”). With the addition of 1 wt. % 1,4-butanediol and 700 ppmtitanium propoxide (Sample 23), both the torque and die pressuredecreased significantly to 66-72% and 30 psi, respectively. The torqueand die pressure could be proportionally adjusted with the change ofreactant and catalyst.

Melt rheology tests were also performed with the control sample andSamples 21-23 on a Göettfert Rheograph 2003 (available from Göettfert inRock Hill, S.C.) at 180° C. and 190° C. with 30/1 (Length/Diameter)mm/mm die. The apparent melt viscosity was determined at apparent shearrates of 100, 200, 500, 1000, 2000 and 4000 s⁻¹. The results are shownin FIG. 4. As indicated, Samples 21-23 had much lower apparentviscosities over the entire range of shear rates than the controlsample. The melt flow index of the sample was determined by the methodof ASTM D1239, with a Tinius Olsen Extrusion Plastometer at 190° C. and2.16 kg. Further, the samples were subjected to molecular weight (MW)analysis by GPC with narrow MW polystyrenes as standards. The resultsare set forth below in Table 8.

TABLE 8 Properties of unmodified and modified Ecoflex F BX 7011 on aZSK-30 Apparent Viscosity (Pa · s at Melt apparent Flow rate Averageshear rate of (g/10 min at Mol. Wt Poly- Sample 1000/s at 190° C.(g/mol) dispersity No. 180° C.) and 2.16 kg) Mw Mn (Mw/Mn) F BX 7011 3214.5 125200 73500 1.7 Control 294 6.8 117900 72100 1.64 21 182 24 10040060500 1.66 22 112 68 82800 46600 1.78 23 61 169 68900 37600 1.83

As indicated, the melt flow indices of the modified resins (Samples21-23) were significantly greater than the control sample. In addition,the weight average molecular weight (M_(w)) and number average molecularweight (M_(n)) were decreased in a controlled fashion, which confirmedthat the increase in melt flow index was due to alcoholysis withbutanediol catalyzed. Table 9, which is set forth below, also lists thedata from DSC analysis of the control sample and Samples 21-23.

TABLE 9 DSC Analysis Glass transition Melting Peak temperature,Temperature, Enthalpy of Sample T_(g) (° C.) T_(m) (° C.) melting (J/g)Ecoflex ® −30.1 123.3 11.7 F BX 7011 Control −31.5 123.5 10.1 21 −35.1127 10.7 22 −32.5 124.7 11.6 23 −34.2 125.1 12

As indicated, Samples 22 and 23 (modified with 1,4-butanediol) exhibitedlittle change in their T_(g) and T_(m) compared with the controlsamples.

Example 5

A modified resin of Example 4 (Sample 23) was used to form a meltblown(“MB”) web. Meltblown spinning was conducted with a pilot line thatincluded a 1.75″ Killion extruder with a single screw diameter of 1.75inches (Verona, N.Y.); a 10-feet hose from Dekoron/Unitherm (RivieraBeach, Fla.); and a 14-inch meltblown die with an 11.5-inch spray and anorifice size of 0.015 inch. The modified resin was fed via gravity intothe extruder and then transferred into the hose connected with themeltblown die. Table 10 shows the process conditions used duringspinning. The temperatures are given in OF.

TABLE 10 1,4-Butanediol modified BFX 7011 MB spinning conditionsExtruder Screw Primary Air Zone 1 Zone 2 Zone 3 Zone 4 Speed TorquePressure Hose Die Temperature Pressure (F.) (F.) (F.) (F.) (rpm) (Amps)(Psi) (F.) (F.) (F.) (Psi) 200 300 310 320 3 4 130 320 350 375 30

A fiber web sample was collected and analyzed with an electronicscanning microscope (“SEM”) at different magnitudes. A micron scale barwas imprinted on each photo to permit measurements and comparisons.FIGS. 5 and 6 show the images of the fiber web at 100× and 500×,respectively. The fiber webs were also collected for tensile analysis.The tensile properties of the modified copolyester meltblown nonwovensamples of different basis weights were tested. The results are listedin Table 11. SD is standard deviation. “Peak Load” is given in units ofpounds-force (Ibf), and “Energy to Peak” is given in units ofpound-force*inch (Ibf*in).

TABLE 11 Modified Ecoflex F BX 7011 MB samples measured with 1″ × 6″strips Basis Peak Load Strain at Peak Energy to Peak Weight (lbf) (%)(lbf * in) Sample (gsm) Mean SD Mean SD Mean SD Machine Direction 11 gsm11.9 0.3 0.06 131.9 12.5 1.28 0.24 22 gsm 23.8 0.62 0.04 225.2 12.2 4.50.22 32 gsm 29 0.91 0.1 310 53.8 9.02 2.5 Cross Direction 11 gsm 11.40.13 0.01 108 13.2 0.36 0.06 22 gsm 23.8 0.35 0.01 187.6 6.9 1.91 0.1132 gsm 28.4 0.5 0.05 241.8 57.3 3.68 1.2

While the invention has been described in detail with respect to thespecific embodiments thereof, it will be appreciated that those skilledin the art, upon attaining an understanding of the foregoing, mayreadily conceive of alterations to, variations of, and equivalents tothese embodiments. Accordingly, the scope of the present inventionshould be assessed as that of the appended claims and any equivalentsthereto.

1. A method for forming a biodegradable polymer for use in fiberformation, the method comprising melt blending a firstaliphatic-aromatic copolyester with at least one alcohol so that thecopolyester undergoes an alcoholysis reaction, the alcoholysis reactionresulting in a second, modified copolyester having a melt flow indexthat is greater than the melt flow index of the first copolyester,determined at a load of 2160 grams and temperature of 190° C. inaccordance with ASTM Test Method D1238-E.
 2. The method of claim 1,wherein the ratio of the melt flow index of the secondaliphatic-aromatic copolyester to the melt flow index of the firstaliphatic-aromatic copolyester is at least about 1.5.
 3. The method ofclaim 1, wherein the ratio of the melt flow index of the secondaliphatic-aromatic copolyester to the melt flow index of thealiphatic-aromatic copolyester is at least about
 50. 4. The method ofclaim 1, wherein the ratio of the apparent viscosity of the firstaliphatic-aromatic copolyester to the apparent viscosity of the secondaliphatic-aromatic copolyester is at least about 1.1, determined at atemperature of 170° C. and a shear rate of 1000 sec⁻¹.
 5. The method ofclaim 1, wherein the ratio of the apparent viscosity of the firstaliphatic-aromatic copolyester to the apparent viscosity of the secondaliphatic-aromatic copolyester is at least about 2, determined at atemperature of 170° C. and a shear rate of 1000 sec⁻¹.
 6. The method ofclaim 1, wherein the second copolyester has a number average molecularweight of from about 10,000 to about 70,000 grams per mole and a weightaverage molecular weight of from about 20,000 to about 125,000 grams permole.
 7. The method of claim 1, wherein the second copolyester has anumber average molecular weight of from about 20,000 to about 60,000grams per mole and a weight average molecular weight of from about30,000 to about 110,000 grams per mole.
 8. The method of claim 1,wherein the polydispersity index of the first and the secondcopolyesters is from about 1.2 to about 2.0.
 9. The method of claim 1,wherein the first and second copolyesters both have a melting point offrom about 80° C. to about 160° C.
 10. The method of claim 1, whereinthe first and second copolyesters both have a glass transitiontemperature of about 0° C. or less.
 11. The method of claim 1, whereinthe melt flow index of the second copolyester is from about 5 to about500 grams per 10 minutes.
 12. The method of claim 1, wherein the meltflow index of the second copolyester is from about 20 to about 250 gramsper 10 minutes.
 13. The method of claim 1, wherein the secondcopolyester has an apparent viscosity of from about 10 to about 500Pascal-seconds, determined at a temperature of 170° C. and a shear rateof 1000 sec⁻¹.
 14. The method of claim 1, wherein the copolyester has anapparent viscosity of from about 30 to about 250 Pascal-seconds,determined at a temperature of 170° C. and a shear rate of 1000 sec⁻¹.15. The method of claim 1, wherein the second copolyester is terminatedwith an alkyl group, hydroxyalkyl group, or a combination thereof. 16.The method of claim 15, wherein the second copolyester has the followinggeneral structure:

wherein, m is an integer from 2 to 10, in some embodiments from 2 to 4′,and in one embodiment, 4; n is an integer from 0 to 18, in someembodiments from 2 to 4, and in one embodiment, 4; p is an integer from2 to 10, in some embodiments from 2 to 4, and in one embodiment, 4; x isan integer greater than 1; y is an integer greater than 1; and R₁ and R₂are independently selected from hydrogen; hydroxyl groups; straightchain or branched, substituted or unsubstituted C₁-C₁₀ alkyl groups; andstraight chain or branched, substituted or unsubstituted C₁-C₁₀hydroxalkyl groups.
 17. The method of claim 16, wherein m and n are eachfrom 2 to
 4. 18. The method of claim 1, wherein the first copolyester ispolybutylene adipate terephalate.
 19. The method of claim 1, wherein thealcohol is employed in an amount of from about 0.1 wt. % to about 20 wt.%, based on the weight of the first copolyester.
 20. The method of claim1, wherein the alcohol is employed in an amount of from about 0.5 wt. %to about 5 wt. %, based on the weight of the first copolyester.
 21. Themethod of claim 1, wherein the alcohol is a monohydric alcohol.
 22. Themethod of claim 1, wherein the alcohol is a polyhydric alcohol.
 23. Themethod of claim 22, wherein the alcohol is a dihydric alcohol.
 24. Themethod of claim 1, wherein a catalyst is employed to facilitate thealcoholysis reaction.
 25. The method of claim 24, wherein the catalystis a transition metal catalyst based on a Group IVA metal, a Group IVBmetal, or a combination thereof.
 26. The method of claim 24, wherein thecatalyst is employed in an amount of from about 50 to about 2000 partsper million of the first copolyester.
 27. The method of claim 1, whereinthe alcoholysis reaction is conducted in the presence of a co-solvent.28. The method of claim 1, wherein melt blending occurs at a temperatureof from about 50° C. to about 300° C. and an apparent shear rate of fromabout 100 seconds⁻¹ to about 10,000 seconds⁻¹.
 29. The method of claim1, wherein melt blending occurs at a temperature of from about 90° C. toabout 180° C. and an apparent shear rate of from about 800 seconds⁻¹ toabout 1200 seconds⁻¹.
 30. The method of claim 1, wherein melt blendingoccurs within an extruder.
 31. The method of claim 1, wherein the secondcopolyester is extruded through a meltblowing die.
 32. A fibercomprising a biodegradable aliphatic-aromatic copolyester terminatedwith an alkyl group, hydroxyalkyl group, or a combination thereof,wherein the copolyester has a melt flow index of from about 5 to about500 grams per 10 minutes, determined at a load of 2160 grams andtemperature of 190° C. in accordance with ASTM Test Method D1238-E. 33.The fiber of claim 32, wherein the melt flow index of the copolyester isfrom about 20 to about 250 grams per 10 minutes.
 34. The fiber of claim32, wherein the copolyester has an apparent viscosity of from about 10to about 500 Pascal-seconds, determined at a temperature of 170° C. anda shear rate of 1000 sec⁻¹.
 35. The fiber of claim 32, wherein thecopolyester has an apparent viscosity of from about 30 to about 250Pascal-seconds, determined at a temperature of 170° C. and a shear rateof 1000 sec⁻¹.
 36. The fiber of claim 32, wherein the copolyester has anumber average molecular weight of from about 10,000 to about 70,000grams per mole and a weight average molecular weight of from about20,000 to about 125,000 grams per mole.
 37. The fiber of claim 32,wherein the copolyester has a number average molecular weight of fromabout 20,000 to about 60,000 grams per mole and a weight averagemolecular weight of from about 30,000 to about 110,000 grams per mole.38. The fiber of claim 32, wherein the copolyester has a melting pointof from about 80° C. to about 160° C.
 39. The fiber of claim 32, whereinthe copolyester has a glass transition temperature of about 0° C. orless.
 40. The fiber of claim 32, wherein the copolyester has thefollowing general structure:

wherein, m is an integer from 2 to 10, in some embodiments from 2 to 4,and in one embodiment, 4; n is an integer from 0 to 18, in someembodiments from 2 to 4, and in one embodiment, 4; p is an integer from2 to 10, in some embodiments from 2 to 4, and in one embodiment, 4; x isan integer greater than 1; y is an integer greater than 1; and R₁ and R₂are independently selected from hydrogen; hydroxyl groups; straightchain or branched, substituted or unsubstituted C₁-C₁₀ alkyl groups; andstraight chain or branched, substituted or unsubstituted C₁-C₁₀hydroxalkyl groups.
 41. The fiber of claim 40, wherein m and n are eachfrom 2 to
 4. 42. The fiber of claim 40, wherein the copolyester isderived from polybutylene adipate terephalate.
 43. A nonwoven webcomprising the fiber of claim
 32. 44. The nonwoven web of claim 43,wherein the web is a meltblown web.
 45. A nonwoven laminate comprising aspunbond layer and a meltblown layer, wherein the spunbond layer, themeltblown layer, or both, are formed from the web of claim 43.